In a mobile communication system, a mobile station is connected with a radio base station unit (hereinafter, to be referred to as a base station) by radio. The mobile station transmits and receives voice data, picture data, e-mail and so on through the base station to and from a counter side station. To meet the condition that the mobile station is in a communicable state, the mobile station must exist in a range in which electromagnetic wave from the base station reaches. A communication possible area extends as the improvement of the mobile communication system advances, and the mobile station can communicate in an extensive area.
However, because the communication becomes possible in the wide area, inconveniences sometimes occur oppositely. For example, in a hospital, there is a possibility that a malfunction of medical equipment is caused due to uplink electromagnetic wave outputted from the mobile station. Also, a call is generally prohibited in places where many persons get together, such as a train and a hotel lobby, and in places where the silence is requested, such as a library, a movie theater and a concert hall, considering inconveniences to the persons. However, it is only prohibited as a moral. If trying to communicate, it is possible to communicate.
On the other hand, a technique is proposed which limits a function of a mobile station in a specific area. For example, In Patent Literature 1 (JP 2000-278755A), a base station forms an electromagnetic wave area in another electromagnetic wave area by another base station and transmits a notice signal which has been spread with a specific spreading code which is different from a spreading code used by the other base station. The function of the mobile station is limited, in case of the reception of the notice signal which has been spread with the specific spreading code, from the base station.
Also, Patent Literature 2 (JP 2008-17105A) discloses a mobile communication system of a CDMA (code division multiple access) type in which communication is possible in a cell covered by a radio base station unit. In the mobile communication system, a mobile relay station converts a scrambling code of a downlink signal received from the radio base station unit into a specific code, and transmits the downlink signal which has been spread with the specific code toward a limitation area to limit communication. A mobile station limits the communication of a predetermined service and notifies the limitation of the communication of the predetermined service with an uplink signal, when receiving the downlink signal of the specific code transmitted from the mobile relay station. A control unit limits the communication of predetermined services to the mobile station when receiving the notification of limitation of the communication of the predetermined services by the uplink signal through the radio base station unit from the mobile station.
As mentioned above, when transmitting a signal, which has been spread with the specific scrambling code, from the mobile relay station, how to determine a scrambling code becomes a problem. This point will be described below.
The scrambling code is a code used to identify the cell. The number of scrambling codes is not infinite and the codes of 512 kinds are prescribed in the W-CDMA cellular system. To prevent interference, the scrambling code of an identical kind is set so as to be not used between cells in a short distance.
When determining the scrambling code, an electromagnetic wave reaching area is estimated for every base station through computer simulation based on the position and equipment of the base station and antenna configuration. The scrambling code of each cell is set so that the scrambling code of an identical kind is assigned to the base stations between which the reaching areas overlap. However, a designer must carry out the setting again when installing a mobile relay station and installing a new base station. Also, because the scrambling code is set using the computer simulation, there is a case that an error exists between the simulation result and an actual electromagnetic wave reaching area. In such a case, the interference has occurred and the design must be performed again. Therefore, the load of the designer becomes heavy. Also, the mobile relay station has a possibility to be installed in an unspecified place. It is difficult to grasp the installation position of the mobile relay station, and the scrambling code used by the mobile relay station for a communication provider.
The technique of determining the scrambling code is described in Patent Literature 3 (JP 2006-140829A). According to a method of setting a scrambling code described in Patent Literature 3, the base station transmits a temporary downlink scrambling code before the determination of a downlink scrambling code. Then, a final downlink scrambling code is determined based on a reception report from an existing mobile station and a peripheral cell list from the base station control unit.
Besides, the techniques which the present inventor could know include Patent Literature 4 (JP H11-220764A).